English

• 0.   Introduction

  Due to the rapid development of the pharmaceutical industry around the world, the widespread use of antibiotics and some irrational discharges led to serious pollution of the water environment, among which tetracycline (TC) is a common pollutant on the surface of the earth, underground, and in drinking water^[1-3]. However, it can fight infections caused by bacteria. The natural decomposition process of this antibiotic is time-consuming and complex, which means that the bioavailability of this antibiotic is minimal. Without a treatment process, it can not be easily decomposed, and most of them can not be absorbed. It eventually enters water bodies in its original form or through metabolites, which has serious implications for human health and ecosystems^[4-5]. Therefore, it is necessary to urgently address the issue of antibiotic contamination of water bodies^[6-8]. Biological treatment, advanced oxidation, and physical and chemical treatment techniques have been studied to prevent antibiotic contamination. Nowadays, photocatalytic technology has become a promising research field due to its green, efficient, and environmentally friendly characteristics^[9-11].

  Silver vanadium oxide (AgVO₃) is one of the most effective metal oxides because it has a stable configuration of silver vanadate compounds and also has multiple crystalline phases even in the case of a single atomic combination^[12], its band gap is only 2.3 eV, and it is responsive and stable to visible light, and AgVO₃ usually plays a great role in the application of photocatalytic degradation because of its narrow band gap and also good crystallinity. However, only silver photocatalyst is not stable^[13-16], because it is susceptible to oxidative decomposition, and if Ag⁺ is reduced to metallic silver (Ag⁰), the active site of the photocatalyst is blocked by Ag⁰, as a result, the photocatalytic activity of the catalyst decreases^[17-18].

  Due to their excellent structure, metal-organic frameworks (MOFs) have shown great application prospects in a large number of nanomaterials^[19-21], making them a hot new material of interest to many researchers. Due to their very high porosity and huge specific surface area, these materials show great application prospects in the fields of energy storage, catalysis, separation, and even environmental remediation^[22]. The combination of semiconductors and MOFs can improve the separation efficiency of light-generated electron-hole pairs and the surface area of the material. ZIF-8 is produced by stirring the metal Zn²⁺ and 2-methylimidazole ligands at room temperature^[23-25] and has attracted researchers for its high thermal stability and excellent water stability.

  In this work, AgVO₃ was synthesized from AgNO₃ and NH₄VO₃^[26-27], and then AgVO₃/ZIF-8 binary composites were prepared by the agitation method. In this case, ZIF-8 material was added while maintaining different molar ratios, especially to increase the photocatalytic activity against the degradation of TC^[28-29]. From the experimental process, we found that the AgVO₃/ZIF-8 composites introduced better photocatalytic activity than the original AgVO₃. This is ultimately due to the improved separation efficiency of optical genic electron-hole pairs^[30-33]. We propose a possible photocatalytic mechanism for AgVO₃/ZIF-8 composites and show in detail how AgVO₃/ZIF-8 binary composites promote the degradation of TC.

  1.   Experimental

  1.1   Materials

  Methanol (CH₃OH), AgNO₃, NH₄VO₃, 2-methylimidazole (C₄H₆N₂), potassium chloride (KCl), 1, 4-benzoquinone (BQ), sodium oxalate (SO), isopropanol (IPA), TC, zinc acetate dihydrate (Zn(CH₃COO)₂·2H₂O), and alcohol (C₂H₅OH) were obtained from Sinopharm Chemical Reagent Co., Ltd. (Shanghai, China). All chemicals were used as received.

  1.2   Preparation

  1.2.1   Synthesis of AgVO₃

  AgVO₃ was obtained according to the previously reported method^[34]: AgNO₃ (2 mmol·L^-1) and NH₄VO₃ (2 mmol·L^-1) were dissolved in 20 mL of deionized water, respectively. Then, the NH₄VO₃ solution was added to the AgNO₃ solution, and after strong stirring for 4 h under the condition of avoiding light, the supernatant was discarded and washed three times with deionized water and ethanol, and finally, the AgVO₃ monomer was obtained by vacuum drying at 80 ℃ overnight.

  1.2.2   Synthesis of ZIF-8 composites

  ZIF-8 was synthesized by a simple stirring method^[35]: 1.5 g of Zn(CH₃COO)₂·2H₂O was dissolved in 70 mL of methanol and noted as solution A, and 3.3 g 2-methylimidazole in 70 mL of methanol was noted as solution B. Solution A and B were sonicated for 20 min until completely dissolved and mixed and stirred for 2 h. The precipitate was centrifuged and washed three times with deionized water and ethanol, dried in an oven at 60 ℃ for 12 h, and then taken out and ground into powder with a mortar.

  1.2.3   Synthesis of AgVO₃/ZIF-8 composites

  0.017 0 g of AgNO₃ was dissolved in 20 mL of deionized water, and 0.227 6 g (1 mmol·L^-1) of ZIF-8 powder was added to sonicate in a homogeneous suspension^[36-38]. 20 mL of NH₄VO₃ (0.011 7 g) solution of upper suspension was added and stirred vigorously in the dark for 4 h. After stirring was completed, the crude product was centrifuged and washed three times with deionized water and ethanol and dried in an oven at 60 ℃ for 12 h to obtain a 10% AgVO₃/ZIF-8 (named 10%-AZ) binary composite, where the 10% is the molar ratio of AgVO₃ and ZIF-8, the A stands for AgVO₃ and the Z stands for ZIF-8^[39]. To study the ratio of compounds with the best effect of TC reduction, the molar ratios of AgVO₃ and ZIF-8 were changed to 5%, 20%, 30%, and 40% to obtain 5%-AZ, 20%-AZ, 30%-AZ, and 40%-AZ, respectively.

  1.3   Characterization

  X-ray diffraction (XRD) patterns were measured on a D8 Advance diffractometer using Cu Kα radiation (λ=0.154 06 nm) at 40 kV with a working current of 40 mA, a scanning range of 5°-80° and a scan rate of 10 (°)·min^-1 (Bruker, Germany). Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) were performed on an S-4800 instrument (HITACHI, Japan). High-resolution transmission electron microscopy (HRTEM) was obtained on the Tecnai G220 instrument (20 kV) (Fei, USA). X-ray photoelectron spectroscopy (XPS) was also found on a Thermo ESCALAB 250XI instrument (ThermoFisher Scientific, USA) using 150 W, monochromatic Al Kα (hν=1 486.6 eV). UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS) was performed on a TU-1901 spectrometer (Persee, China). The electron spin resonance (ESR) signals of free radicals were processed on an ESR spectrometer A300-10/12 (Bruker, Germany) using the capture reagent. Photoluminescence (PL) spectroscopy was demonstrated by the Analytical Instruments FLS-980 spectrophotometer (Edinburgh, UK).

  1.4   Photocatalytic test

  The photocatalytic activity of AgVO₃/ZIF-8 was evaluated in a photocatalytic reactor using a 250 W xenon lamp without a UV-cut filter as a simulated solar light source. 10 mg of photocatalyst was added to 100 mL of 10 mg·L^-1 TC solution and sonicated. Stir for 30 min in the dark to ensure the adsorption-desorption equilibrium between the photocatalyst and TC. After irradiating the reaction, 4 mL of suspension was degraded every 5 min, and particles were filtered out with a 0.22 μm filter membrane in each sampling. Deionized water was used as the reference solution and further analyzed using a UV-Vis spectrophotometer at 357 nm to detect the concentration of the TC solution.

  1.5   Photoelectrochemical measurement

  Transient photocurrents and electrochemical impedance spectroscopy (EIS) were measured on the CHI-700D potentiostat (Shanghai Chenhua Analytical Instrument Co., Ltd.) using a three-electrode system consisting of an indium tin oxide (ITO) electrode, a Pt electrode, and an Ag/AgCl electrode. Using ITO conductive glass as the working electrode, 1 mg of photocatalyst was dispersed in Nafion ethanol solution, then ultrasonicated to form a homogeneous solution, and then the liquid was evenly coated on one end of the ITO glass to form a 1 cm×1 cm test area. A 300 W xenon lamp equipped with a 400 nm bandpass filter was used as the visible-light lamp. 0.5 mol·L^-1 Na₂SO₄ aqueous solution served as the electrolyte.

  2.   Results and discussion

  2.1   Characterizations

  The XRD patterns of AgVO₃, ZIF-8, and the composites are shown in Fig. 1. AgVO₃ showed strong characteristic peaks at 12.40°, 17.22°, 24.95°, 27.50°, 28.22°, 31.43°, 32.02°, and 32.82°, corresponding to the diffraction planes of (110), (200), (220), (310), (221), (221), (131), and (002). While in the XRD pattern of ZIF-8 (PDF No.062-1030), the characteristic peaks at 7.22°, 10.32°, 12.66°, 14.62°, 16.42°, 17.98°, 24.42°, and 26.62° could be found. The AgVO₃/ZIF-8 binary composites showed the characteristic peaks of AgVO₃ (PDF No.089-4396), and the two characteristic peaks of 7.22° and 12.66° of ZIF-8 were observed.

  Figure 1

  

  Figure 1.  XRD patterns of AgVO₃, ZIF-8, and AgVO₃/ZIF-8 composites

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  The morphology of 10%-AZ was revealed by SEM (Fig. 2a-2c). In the structure of AgVO₃/ZIF-8, the nanosheet AgVO₃ can be attached to the surface of ZIF-8 after compositing with AgVO₃. The dodecahedral structure of ZIF-8 can be noticed to be a bit rough because of the decoration of the nanosheet AgVO_3. The EDS spectrum was tested. The Ag, V, and O elements from AgVO₃ and Zn and N elements from ZIF-8 were found to be distributed uniformly, indicating that AgVO₃ and ZIF-8 were successfully constructed (Fig. 2d).

  Figure 2

  

  Figure 2.  SEM images (a, b), elemental mappings (c), and EDS spectrum (d) of 10%-AZ

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  The topography of 10%-AZ was further characterized using HRTEM. The structure of the composite material was confirmed by laminating nanosheet AgVO₃ on the surface of the regular dodecahedron ZIF-8 by interfacial contact (Fig. 3a). In addition, the plaid with an interface distance was measured at 0.31 nm, which corresponds to the AgVO₃ (221) plane (Fig. 3b).

  Figure 3

  

  Figure 3.  HRTEM images of 10%-AZ

  b is an enlarged view of the red box in a.

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  The XPS was used to identify the elemental and valence states of the 10%-AZ composite. In the survey spectrum, peaks of N, O, V, Zn, and Ag were observed, indicating the presence of these elements in 10%-AZ (Fig. 4a). Fig. 4b and 4c show the high-resolution XPS spectra of N and O, with binding energies of 398.88 and 531.48 eV, respectively. The electron binding energies of V2p are 517.38 and 524.98 eV, which correspond to V2p_5/2 and V2p_3/2 respectively, indicating that V³⁺ from AgVO₃ (Fig. 4d). The Zn2p peaks with two electron binding energies of 1 021.58 and 1 044.68 eV can be corresponded to Zn2p_3/2 and Zn2p_1/2 of Zn²⁺, which is derived from ZIF-8 (Fig. 4e). In Fig. 4f, the two peaks of Ag3d at 368.58 and 374.68 eV belong to Ag3d_3/2 and Ag3d_5/2, is attributed to the Ag⁺ from AgVO₃.

  Figure 4

  

  Figure 4.  XPS spectra of 10%-AZ: (a) survey spectrum; (b) N1s; (c) O1s; (d) V2p; (e) Zn2p; (f) Ag3d

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  The light absorption properties of the pristine AgVO₃, ZIF-8, and 10%-AZ were studied by the UV-Vis DRS (Fig. 5a). AgVO₃ and ZIF-8 showed absorption edges at 582 and 245 nm, respectively. After forming the composite material, 10%-AZ showed an absorption edge at 392 nm. The band gap (E_g) of the selected sample can be calculated by αhν=A(hν-E_g)^n/2, where α, h, ν, A, and n represent the absorption coefficient, Planck′s constant, light frequency, the optical frequency constant, and the type of semiconductor material, respectively. The band gaps of AgVO₃ and ZIF-8 could be calculated as 2.74 and 5.24 eV, while the band gap of 10%-AZ was 3.63 eV (Fig. 5b).

  Figure 5

  

  Figure 5.  UV-Vis DRS (a) and calculated bandgaps (b) of AgVO₃, ZIF-8, and 10%-AZ

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  2.2   Photocatalytic activity evaluation

  The photocatalytic performance of AgVO₃, ZIF-8, and AgVO₃/ZIF-8 composites was evaluated by TC degradation under simulated sunlight irradiation. The relative degradation rate constant was calculated using a first-order kinetic equation ln(ρ₀′/ρ)=kt^[40-42], where t, k, ρ₀′, and ρ are the degradation time, the rate constant of the reaction, the initial mass concentration after dark adsorption equilibrium, and the mass concentration at the light time t, respectively. AgVO₃ adsorbed about 14.2% TC in the first 30 min in the dark and degraded about 21.5% TC after 60 min irradiation; ZIF-8 could degrade 64.9% of TC. ZIF-8 has a wide specific surface area, which facilitates the provision of a large number of active sites, enhances the interfacial contact between the catalyst and the reactants, and enhances the effectiveness of the catalytic process. In addition, the uniform pore structure of ZIF-8 allows reactant molecules to be concentrated within its porosity via physical adsorption, thereby establishing a locally high concentration environment on the catalyst surface, helping to increase reaction kinetics and optimize selectivity. When AgVO₃ was combined with ZIF-8, the adsorption capacity of the binary composite was enhanced, and 10%-AZ could adsorb up to 41.6% of the TC in the dark. After irradiation, 5%-AZ, 10%-AZ, 20%-AZ, 30%-AZ, and 40%-AZ degraded 58.2%, 75.0%, 72.4%, 65.6%, and 70.1% TC, respectively (Fig. 6a).

  Figure 6

  

  Figure 6.  Photocatalytic degradation curves of TC under visible light irradiation (a) and corresponding kinetic curves (b) of AgVO₃, ZIF-8, and AgVO₃/ZIF-8

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  A first-order kinetic model was used to further investigate the photocatalytic efficiency of the samples. The k of AgVO₃, ZIF-8, 5%-AZ, 10%-AZ, 20%-AZ, 30%-AZ, and 40%-AZ were calculated as 0.004 000, 0.011 47, 0.008 400, 0.013 53, 0.013 43, 0.011 84, and 0.013 58 min^-1, respectively (Fig. 6b). The k of 10%-AZ (0.013 53 min^-1) was 3.4 times that of AgVO₃ (0.004 000 min^-1). Finally, the results show that all five binary composites had a significant increase compared to the original AgVO₃. The binary composites showed the enhanced degradation efficiency of TC. Because of the high catalytic degradation efficiency and low material cost, binary materials with a molar ratio of 10% were more suitable for practical use, which means that 10%-AZ was treated as the best two-component composite. An encapsulated summary of AgVO₃-based photocatalysts is shown in Table 1, showing that the 10%-AZ composite exhibited superior photocatalytic effects compared to other photocatalysts described in the literature.

  Table 1

  

  Table 1.  Comparison with reported AgVO₃ based photocatalysts for degradation of TC

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  Sample	ρcatalyst / (g·L-1)	ρTC / (mg·L-1)	Degradation efficiency / %	t / min	k / min-1	Light source	Ref.
  AgVO3/MoS2	0.1	10	73	180	0.008 70	350 W Xe lamp	[43]
  Ag-AgVO3/g-C3N4	0.2	30	83.6	120	0.029 8	300 W Xe lamp	[44]
  AgVO3/Ag2S	0.3	20	72	120	0.009 82	300 W Xe lamp	[45]
  AgVO3/Bi4Ti3O12	0.3	5	57	60	0.016 11	300 W Xe lamp	[46]
  KBi6O9I/Ag-AgVO3	1	50	83.5	120	0.024 6	400 W Xe lamp	[47]
  AgVO3/ZIF-8	0.1	10	75.0	60	0.013 53	250 W Xe lamp	This work

  The effects of photocatalysts with different mass concentrations were then studied with 10%-AZ. When the amount of photocatalyst was increased, the adsorption capacity of 10 mg·L^-1 TC also increased (Fig. 7a). Therefore, when the dosage of the photocatalyst was increased from 0.2 to 0.6 g·L^-1, the degradation efficiency was improved from 67.23% to 81.23% (Fig. 7a). As a result, photocatalysts with a mass concentration of 0.6 g·L^-1 had the highest degradation efficiency due to the increase in the amount of photocatalyst with an increase in active sites. The k values were 0.013 53, 0.010 35, 0.013 20, and 0.012 82 min^-1 when the dosages were 0.1, 0.2, 0.4, and 0.6 g·L^-1 (Fig. 7b). The catalyst had the maximum k value with the dosage of 0.1 g·L^-1 (k=0.013 53 min^-1). Though the catalyst with the dosage of 0.6 g·L^-1 had the best degradation efficiency, its k value was not better than that of a dosage of 0.1 g·L^-1, resulting from the more photocatalyst and the more opacity of the TC solution having a certain inhibitory effect on the performance of the photocatalyst.

  Figure 7

  

  Figure 7.  Photocatalytic degradation curves of TC in the presence of different 10%-AZ amounts (a) and corresponding kinetic curves (b); Photocatalytic degradation curves of TC in the different masses of KCl (c) and corresponding kinetic curves (d)

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  Ion resistance is also an important factor in evaluating the further application of photocatalysts. KCl (5, 10, 20, 30 mg) was used to determine whether the degradation efficiency of 0.1 g·L^-1 10%-AZ on 10 mg·L^-1 TC was affected by different ionic contents. When the mass of KCl was increased to 30 mg, the effect of ionic content on the catalytic effect was less pronounced compared to a blank control without the addition of KCl (Fig. 7c). This proved that the photocatalytic activity of the AgVO₃/ZIF-8 composite photocatalyst is not affected in a specific ionic content range. When 0, 5, 10, 20, and 30 mg of KCl were added, the k values were 0.013 53, 0.013 13, 0.013 28, 0.011 15, and 0.013 99 min^-1, respectively (Fig. 7d). When 30 mg KCl was added, the k was the maximum value, but the increase was not obvious compared to the absence of KCl, and the k of other ion concentrations was not much different from that without KCl. This supports the conclusion that the 10%-AZ composite has little effect on the degradation of TC in the presence of different ion concentrations.

  The trapping experiment with active species was carried out to investigate the photocatalytic mechanisms. The degradation curves of 10 mg·L^-1 TC by adding IPA, BQ, and SO as active trapping agents of ·OH, ·O₂^- and hole h⁺ photocatalysts is shown in Fig. 8. IPA and BQ had a significant effect on the photocatalytic degradation effect, and the degradation efficiencies of TC was decreased to 61.7% and 61.4%, respectively, and the degradation efficiency was reduced by about 13% compared with the addition without trapping agents (Fig. 8a). At the same time, SO also had effect on photocatalytic degradation. The degradation efficiency of TC was 70.5%, which was not much different from that without trapping agents. The k was 0.011 70 min^-1 when SO was added. With the addition of BQ and IPA, the k values were reduced to 0.010 07 and 0.008 890 min^-1. Therefore, it can be concluded that in the photocatalytic degradation of TC by 10%-AZ binary composites, ·OH and ·O₂^- are essential active substances, and h⁺ has little effect on photocatalytic degradation.

  Figure 8

  

  Figure 8.  Trapping experiment for photocatalytic degradation of 10 mg·L^-1 TC (a) and corresponding kinetic curves (b)

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  To confirm the stability of the photocatalyst, a 10%-AZ composite photocatalytic material was selected as the experimental subject (Fig. 9a). Following each cycle of photocatalytic degradation, the samples were subjected to centrifugation, subsequent rinsing, and drying processes to perpetuate the evaluation of TC photocatalytic degradation. After completing four cycles, the degradation efficiency of the 10%-AZ composite dropped from 75.0% to 66.7%, and the associated loss was 8.3%. The degradation efficiency of TC in the sample showed a decrease during the cycle test, but this reduction was considered insignificant, considering the decrease in the sample during the operating procedure. To further explore the variation of the synthesized photocatalyst, the XRD test was repeated after four cycles (Fig. 9b). After four degradation processes, no significant changes were seen in the XRD patterns of 10%-AZ. Therefore, it can be inferred that this material has commendable reusability and chemical stability in the context of TC degradation.

  Figure 9

  

  Figure 9.  Recycle experiment over 10%-AZ of TC degradation (a) and XRD patterns of 10%-AZ before and after photocatalytic degradation of TC (b)

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  The ESR measurements were further used to explore the production of active species in the 10%-AZ photocatalytic reaction. The generation of ·O₂^- and ·OH can be detected by adding DMPO (5, 5-dimethyl-1-pyrroline-N-oxide) molecules to form the corresponding ESR signals. The ESR signals of DMPO-·O₂^- and DMPO-·OH were not found in the dark (Fig. 10). However, DMPO-·O₂^- and DMPO-·OH adducts were able to detect characteristic signals after 10 min of visible light exposure, indicating that ·O₂^- and ·OH were both active substances in the photodegradation process of TC above 10%-AZ, which was consistent with the results of the trapping experiment.

  Figure 10

  

  Figure 10.  ESR spectra of DMPO-·O₂^- (a) and DMPO-·OH (b) adducts over 10%-AZ

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  10%-AZ showed an enhanced photocurrent response compared to the pristine AgVO₃ and ZIF-8 (Fig. 11a). To investigate the separation efficiency of the electron-hole pairs, the EIS was further measured (Fig. 11b). As shown in the EIS, the radius of 10%-AZ was smaller than that of the original AgVO₃ and ZIF-8, indicating that the charge transfer efficiency of 10%-AZ was higher than the pristine materials. The results of photocurrent and EIS showed that after building the composite, the separation efficiency of the charge carrier can be improved.

  Figure 11

  

  Figure 11.  Transient photocurrent response curves (a) and EIS (b) of AgVO₃, ZIF-8, and 10%-AZ

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  The PL measurements were performed to assess the transfer and separation of electron-hole pairs during photocatalysis. The PL spectra of AgVO₃, ZIF-8, and 10%-AZ under excitation at 320 nm are shown in Fig. 12. AgVO₃ and ZIF-8 exhibited stronger emission intensity due to the more rapid recombination of photogenic electron-hole pairs, while 10%-AZ exhibited the lowest intensity, which might have happened due to the smallest number of photogenic electron-hole pairs produced under visible light irradiation. After the construction of AgVO₃/ZIF-8, the PL strength of the composites was lower than that of ZIF-8.

  Figure 12

  

  Figure 12.  PL spectra of AgVO₃, ZIF-8, and 10%-AZ

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  Finally, a reasonable photocatalytic mechanism can be explained according to the above results. ZIF-8 cannot be activated by simulated sunlight to move electrons from the valence band (VB) to the conduction band (CB). It acts as a porous template to disperse AgVO₃ on the surface and increase the contact area and the probability that it can increase photocatalytic activity. AgVO₃, on the other hand, can be activated by simulated sunlight, resulting in the formation of holes in VB and electrons in CB. Electrons from the CB of AgVO₃ produced an active ·O₂^- species, and the VB holes of AgVO₃ produced an active ·OH species (Fig. 13).

  Figure 13

  

  Figure 13.  Schematic mechanism of photocatalytic TC degradation over AgVO₃/ZIF-8 irradiated with simulated sunlight

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  3.   Conclusions

  In this study, we synthesized a series of AgVO₃/ZIF-8 composites with enhanced photocatalytic performance of TC in visible light descent compared to the original AgVO₃ monomer and ZIF-8 materials. The excellent specific surface area and regular pore structure of ZIF-8 have greatly improved the photocatalytic degradation performance of AgVO₃/ZIF-8 composites. AgVO₃ and ZIF-8 had the highest photocatalytic activity when the molar ratio was 10%, with a degradation rate of 75.0%. The enhancement of photocatalytic activity can be attributed to the improvement in the separation of photogenerated electron-hole pairs and the active ·OH and ·O₂^- species generated in ESR measurement and capture experiments. In addition, AgVO₃ can also be used as a silver source for silver particles, reducing O₂ to ·O₂^-.

  Credit authorship contribution statement: ZHU Min: Project administration, formal analysis, writing-original draft, writing-review & editing. WANG Yuxin: Writing-original draft. LI Xiao: Investigation, software. XU Yaxu: Investigation. ZHU Junwen: Software. WANG Zihao: Investigation. ZHU Yu: Supervision, project administration, data curation, writing-review & editing. HUANG Xiaochen: Methodology. XU Dan: Investigation. Abul Monsur Showkot Hossain: Writing-review & editing.

  
  Acknowledgments: QingLan Project of Jiangsu Province, Major Project of Basic Science (Natural Science) Research in Higher Education Institutions of Jiangsu Province (Grant No.23KJA530002), Technology Support Program (Social development) of Taizhou (Grant No.TN202424). Declaration of competing interest: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
  Data availability: Data will be made available on request.
  
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• 

  Figure 1  XRD patterns of AgVO₃, ZIF-8, and AgVO₃/ZIF-8 composites

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  Figure 2  SEM images (a, b), elemental mappings (c), and EDS spectrum (d) of 10%-AZ

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  Figure 3  HRTEM images of 10%-AZ

  b is an enlarged view of the red box in a.

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  Figure 4  XPS spectra of 10%-AZ: (a) survey spectrum; (b) N1s; (c) O1s; (d) V2p; (e) Zn2p; (f) Ag3d

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  Figure 5  UV-Vis DRS (a) and calculated bandgaps (b) of AgVO₃, ZIF-8, and 10%-AZ

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  Figure 6  Photocatalytic degradation curves of TC under visible light irradiation (a) and corresponding kinetic curves (b) of AgVO₃, ZIF-8, and AgVO₃/ZIF-8

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  Figure 7  Photocatalytic degradation curves of TC in the presence of different 10%-AZ amounts (a) and corresponding kinetic curves (b); Photocatalytic degradation curves of TC in the different masses of KCl (c) and corresponding kinetic curves (d)

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  Figure 8  Trapping experiment for photocatalytic degradation of 10 mg·L^-1 TC (a) and corresponding kinetic curves (b)

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  Figure 9  Recycle experiment over 10%-AZ of TC degradation (a) and XRD patterns of 10%-AZ before and after photocatalytic degradation of TC (b)

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  Figure 10  ESR spectra of DMPO-·O₂^- (a) and DMPO-·OH (b) adducts over 10%-AZ

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  Figure 11  Transient photocurrent response curves (a) and EIS (b) of AgVO₃, ZIF-8, and 10%-AZ

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  Figure 12  PL spectra of AgVO₃, ZIF-8, and 10%-AZ

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  Figure 13  Schematic mechanism of photocatalytic TC degradation over AgVO₃/ZIF-8 irradiated with simulated sunlight

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  Table 1.  Comparison with reported AgVO₃ based photocatalysts for degradation of TC

  Sample	ρcatalyst / (g·L-1)	ρTC / (mg·L-1)	Degradation efficiency / %	t / min	k / min-1	Light source	Ref.
  AgVO3/MoS2	0.1	10	73	180	0.008 70	350 W Xe lamp	[43]
  Ag-AgVO3/g-C3N4	0.2	30	83.6	120	0.029 8	300 W Xe lamp	[44]
  AgVO3/Ag2S	0.3	20	72	120	0.009 82	300 W Xe lamp	[45]
  AgVO3/Bi4Ti3O12	0.3	5	57	60	0.016 11	300 W Xe lamp	[46]
  KBi6O9I/Ag-AgVO3	1	50	83.5	120	0.024 6	400 W Xe lamp	[47]
  AgVO3/ZIF-8	0.1	10	75.0	60	0.013 53	250 W Xe lamp	This work

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